Infrared Based Peeling of Fruits and Vegetables

ABSTRACT

A method and apparatus for infrared peeling of fruits and vegetables is disclosed herein.

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 61/418,859, filed Dec. 1, 2010 which is herein incorporated byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates to an infra-red method and apparatus forremoval of peel from fruits and vegetables without the use of chemicalsor steam. Unique final product microstructure is achieved through thisprocess, resulting in improved final product quality.

BACKGROUND OF THE INVENTION

Lye peeling is traditionally used in fruit and vegetable processingindustry due to its ability to produce high quality products. However,the process yields large amount of wastewater with high salinity whichhas a negative impact on the environment (Garcia and Barrett, 2006a, b;Masanet et al., 2007; Schlimme et al., 1984; Wongsa-Ngasri, 2004). Thealternative process of steam peeling results in deteriorated productquality factors including appearance, higher loss in firmness, and loweryield compared to the regular lye peeling method (Garcia and Barrett,2006a). Furthermore, the process of mechanical peeling by knife cuttingsuffers from reduced final product yield.

Alternative peeling techniques such as enzymatic peeling, flame-peeling,vacuum-peeling, acid-peeling, freeze-peeling, calcium chloride peeling,and peeling with ohmic heating have been studied on different fruits andvegetables (Rouhana and Mannheim, 1994; (Ben-Shalom and Pinto, 1986;Pretel et al., 1997; Toker and Bayndrl, 2003). Other researchers havealso studied modified conventional methods, such as high pressure steampeeling with flash cooling, lye-steam peeling, dry-caustic peeling, andfreeze-heat peeling (Smith et al., 1980). However, successfulcommercialization of these methods has been hampered because of highequipment and processing costs or other reasons such as reduced finalproduct quality.

Infrared (IR) radiation is energy in the electromagnetic wave form thatcan be used for thermal processing of foodstuff (Pan et al., 2008). Ourinvestigations have recently demonstrated the potential of using IR asan alternative and sustainable tomato peeling technology (Li et al.,2009). Tomato peel loosening involves the loss of rigidity andseparation of several cell layers between exocarp and mesocarp due tothe breakdown of pectin and the formation of cracks on the tomatosurface because of the reduced skin strength. During IR peeling, thermaleffects are thought to control the release of the skin although theexact mechanism is unknown. This is mechanistically contrary to thetraditional lye peeling whereby the lye solution penetrates the skin anddissolves the pectic and hemicellulosic material in the cell walls viadiffusion and removes the pectin which results in the weakening of thenetwork of cell wall and causes the release of the skin (Das andBarringer, 2005). The mechanism for steam peeling is similar to lyepeeling, but without dissolving related to the lye. Resulting loss oftissue from steam peeling is typically high as is loss of firmness inthe final product, making it less desirable than lye peeling. IR peelingis also different from knife cutting which typically removes arelatively thick layer of tissue rather than just the skin of fruits andvegetables. The novel IR peeling method and use of apparatus in thisinvention result in products with surprisingly good quality, highyields, as well as excellent color, texture and flavor.

Although prior studies have investigated the potential of IR forpeeling, none have been successful without the use of some caustic/lyein addition to application of IR. This invention for the first timeclaims the use of IR alone as a highly effective method for peelingfruits and vegetables. Previous studies on IR dry caustic peelingproposed that since IR does not require a heating medium for thedelivery of energy to the product, such as water, that the process benamed “dry peeling” (Hart et al., 1970). The application of IRdry-caustic peeling was studied for white potatoes and peaches and theresults exhibited significant decreases in peeling loss, usage ofcaustic lye and generation of wastewater (Sproul et al., 1975). Theseexamples used both IR and caustic and differ from the claimed inventionin that the claimed invention for the first time uses only IR forpeeling purposes.

Because of the high heat delivery capability and low penetration depth,IR is a very suitable heating method for efficiently loosening the skinand thereby peeling of fruits and vegetables. Uniform rapid heating ofthe fruits and vegetables during IR treatment was not previouslyachieved and is necessary to produce good quality end products. Thisinvention solves these and other previously insurmountable challengesrelated to IR peeling and enables the user for the first time to takeadvantage of the IR process to efficiently peel fruits and vegetablescommercially.

SUMMARY OF THE INVENTION

An embodiment of the invention is a product with a microstructurecontaining a ratio of cell wall expansion within the interior of theproduct that is not observed through other peeling processes.

An embodiment of the invention is an apparatus containing concaveinfra-red emitters with the appropriate composition, wavelength,intensity, configuration and temperature encased in a heat reflectivemetal housing with or without air circulation controls to provideuniform heating to the surfaces of fruits and vegetables in order topromote peeling.

A further embodiment of said apparatus is the use of rotation of thefruit or vegetable upon exposure to the emitters and/or use of conveyorsand belts adapted to the shape of the fruit or vegetable to providemaximum and uniform exposure to the heat from the emitters.

Another embodiment is of the apparatus is a reflective metal housingthat maximizes heat transfer and containment in the apparatus foroptimum peeling.

A further embodiment is the inclusion of air circulation in the IRapparatus to promote uniform high quality products.

Another embodiment is the use of vacuum during IR treatment to assistpeeling of fruits and vegetables.

An additional embodiment is a method of dry peeling fruits andvegetables without the use of chemicals or steam by exposing the fruitand vegetables to the apparatus' embodied above with the appropriatecomposition, wavelength, intensity, configuration and temperature for atime sufficient to promote peeling.

Another embodiment is the use of surfactant mixtures and or to assist ininfrared peelingSurface active agents or surfactants aremulti-functional chemical entities. Ionic (anionics, cationics andamphoterics) and Non-ionic surfactants are most commonly used. Non-ionicsurfactants commonly include mono- and di-glycerides, derivatives suchas acetylated, succinylated and diacetylated tartaric esters ofdistilled monoglycerides, lactylated esters, sorbitan esters,polysorbates, propylene glycol esters, sucrose esters and polyglycerolesters. One specific example is ethyl oleate or oleic acid ethyl ester.

Another embodiment is the use of vacuum chamber after IR heating topromote the separation of the peels and flesh.

Another embodiment is the use of scrubbers such as discs or abrasives toassist in removal of the peel from the infrared treated fruit orvegetables.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing of a catalytic IR emitter with rotating produce.

FIG. 2 is a drawing of an IR heating for peach peeling.

FIG. 3 is a graph of the linear relationship between peach weight andsize.

FIGS. 4A and 4B are graphs of peeling performance and product qualitywith different IR heating times.

FIG. 5 is a graph of the depth of heating ring at different timeintervals.

FIG. 6 is a graph of percent peelability for hand scrubbed and sprayoff.

FIG. 7 is a graph of peeling yield for different time intervals of lyeand infrared peeling.

FIG. 8 is a graph of firmness for small medium and large fruit sizeswith IR and caustic peeling.

FIG. 9 is a graph of color change for small medium and large fruit sizeswith IR and caustic peeling.

FIG. 10 is a graph of moisture loss of small, medium and large fruitsizes with IR heating.

FIG. 11 is a graph of peelability for IR and caustic with varyingemitter gaps.

FIG. 12 is a graph of peeling yields for IR and caustic with varyingemitter gaps.

FIG. 13 is a graph of firmness in different gap sizes of emitters.

FIG. 14 is a graph of color change in different gap sizes of emitters.

FIG. 15 is a graph of surface temperature of blossom, stem and suture attime intervals.

FIG. 16 is a graph of internal temperature of varying skin depths.

FIG. 17 is a photo of an infrared peeling apparatus utilizing a rotatingplatform.

FIGS. 18 A and B are photos of a peeled Bartlett pear after 60 and 45seconds of infrared treatment.

FIG. 19 is a photo of peeled skin from Bartlett pear after 60 and 45seconds of infrared treatment, respectively.

FIGS. 20A-C are photos of a peeled Bartlett pear after 30, 25 and 15seconds of infrared treatment and peel remnants.

FIGS. 21A-D are scanning electron micrograph (SEM) photos of outersurface of tomato skin: (A) fresh control; (B) IR treated tomato; (C)Lye treated tomato; (D) Steam treated tomato skin.

FIGS. 22A-D are SEM photos of cross-sectional views of tomato dermalsystem: (A) fresh control; (B) IR treated tomato; (C) Lye treatedtomato; (D) Steam treated tomato skin.

FIGS. 23A-D are SEM photos of cross-sectional views of tomato exocarptissue: (A) fresh control; (B) IR treated tomato; (C) Lye treatedtomato; (D) Steam treated tomato skin.

FIGS. 24 A-C are SEM photos of the outer surface of pear skin: (A) freshcontrol; (B) IR heating; (C) lye treatment.

FIGS. 25 A-D are SEM photos of cross section of pear pericarp: (A) freshcontrol; (B) IR heating; (C) lye treatment; (D) knife-cut.

FIGS. 26 A-D are SEM photos of pear cells: (A) fresh control; (B) IRheating; (C) lye treatment; (D) knife-cut.

FIGS. 27 A and B are drawings of an alternate array emitterconfiguration, bottom and top view.

FIG. 28 is a drawing of an alternate “z” emitter configuration.

DESCRIPTION OF THE INVENTION

The terminology used in the description of the invention herein is fordescribing particular embodiments only and is not intended to belimiting of the invention. As used in the description of the inventionand the appended claims, the singular forms “a,” “an,” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise.

“Fruit and vegetables” as defined herein is inclusive of but not limitedto skin containing produce, such as pear, peach, apricot, apple, grape,cherries, tomato, bananas, potato, eggplant, tomato, cucumber, zucchini,oranges, lemons, grapefruit.

Unless otherwise indicated, all numbers expressing quantities ofingredients, properties such as molecular weight, reaction conditions,and so forth as used in the specification and claims are to beunderstood as being modified in all instances by the term “about.”Accordingly, unless otherwise indicated, the numerical properties setforth in the following specification and claims are approximations thatmay vary depending on the desired properties sought to be obtained inembodiments of the present invention. Notwithstanding that the numericalranges and parameters setting forth the broad scope of the invention areapproximations, the numerical values set forth in the specific examplesare reported as precisely as possible. Any numerical values, however,inherently contain certain errors necessarily resulting from error foundin their respective measurement.

An embodiment of the apparatus employs a delivery belt or conveyor totransport the fruit and vegetables to a space between two infra-redemitters or lateral exposure to one IR emitter. Optionally, the fruit orvegetable may be supported for rotation within the emitter heat field(FIG. 1). The emitters are non glass and may be catalytic, ceramicdepending on the targeted fruit or vegetable. The orientation of theemitter with respect to the fruit or vegetable may be horizontal (FIG.2), vertical or multidirectional. The selection of emitters is based onthe properties of the particular fruit or vegetable. The surface of theemitters may be flat or as a preferred embodiment possess a concavesurface wherein the relative degree of curvature of the emitter isshaped in relation to the targeted fruit or vegetable to maximize heatuniformity to the surface of the peel. The degree of curvature of theemitter may be from 1° to 180° depending on the area and shape of thefruit or vegetable within the emitter heat field. An additionalembodiment for achieving uniformity is by configuring emitters in anarray or zigzag(z) pattern. Referring to FIGS. 27 A & B, an arraypattern consists of multi-sectional contiguously attached emitterswherein the total emission area 1 of the array is flat or concave inshape and the emitters in each section are offset relative to the otherattached section(s) in depth, lateral orientation or both.

The z pattern employs sections of emitters which contiguously intersectalong the longitudinal edges of the emitters forming a z pattern perthree intersecting line edge sections of the emitters when viewed alongan x or y axis orientation of the emitter (FIG. 28, 1 is heatingsurface, 2 is top of emitter). The z pattern may also be implemented inan emitter fashioned or molded from a single sheet or cast of metallicor ceramic material. Emitters conforming to a z pattern may also containa degree of curvature to maximize infrared exposure to the food. Thedegree of curvature for the array and z pattern will depend on the sizeshape and quantity of food that is being exposed within the field ofinfrared radiation.

Depending on the skin thickness and sensitivity of the skin to heat andheating time, complete peeling for fruits and vegetables can be achievedby heating using a constant high IR emitter temperature or a variable IRemitter temperature. For fruits and vegetables with thin peel, such aspeach, variable IR emitter temperature may be needed to avoid burning ofthe peel. Fruits and vegetables are heated with high temperatureemitters first, followed by heating using the emitters with reducedtemperature. Constant high IR emitter temperature heating is mostappropriate for thick skinned produce or produce with low heatsensitivity. Additionally, scrubbers or abrasive discs and pads may beemployed during or after variable or constant IR emitter temperaturepeeling for thick skinned produce or produce with low heat sensitivity.

Single-sided heating or double-sided heating can be used based on thedesign of the heating system and characteristics of fruits and vegetableto be heated. The shaped of the emitter is concave, wherein the degreeof curvature may be adjusted to the particular fruit or vegetable tomaximize heat exposure. The emitter surface temperature is in the rangeof 200-850° C. with corresponding wavelengths of 6.1-2.8 microns. Thesurface emitter temperature is inversely proportional to the heatingtime of the fruit or vegetable. The preferred emitter surfacetemperature is in the range of 200-750° C. (with correspondingwavelengths of 6.1-2.6 microns). The distance between the fruit surfaceand the emitter surface is between 5-40 mm. The preferred distancebetween the fruit surface and the emitter surface is between 5-15 mm.The shortest distance between fruit surface and emitter surface shouldnot be less than 5 mm. The surface temperature of fruits and vegetablesduring IR heating is in the range of 70-100° C., preferably between85-95° C. A heat reflective metal housing encasing the emitter(s) mayalso be employed to increase the efficiency of the IR zone of peeling.

When IR application occurs with the fruit on a conveyor belt, apreferred embodiment is the use of wells or recessions 3, FIG. 28, inthe belt which hold and conform to the general shape of the produce topromote rotation and heat uniformity of the fruits and vegetables.

A further embodiment is the use of a vacuum chamber after IR heating tocrack the peel/skin off of the fruits and vegetables. Vacuum enhancesheat penetration and may be in the range of 20-30 inches Hg.

Fruits or vegetables subjected to infra-red peeling of the embodimentsset forth above, exhibit a distinguishing feature of an intercellular(IEC) to intracellular (IAC) area (IIP) of 25% to 35%, as measured byscanning electron microscope (SEM), representing an IEC/IAC ratio of 2to 5 times that of lye, steam and knife peeled methods (Tables 1 and 2).The IR treated sample has the highest IIP due to the thermal expansionof cell wall and middle lamella. Knife cut samples have a similar IIP tofresh control which is also the lowest IIP.

TABLE 1 SEM quantification for tomatoes Intercellular/ Ratio ofintracellular IR/ percentage (%) Treatment Treatment 9.4 Fresh 3.1* 29.6IR 1.0 14.7 Lye 2.0 6.62 Steam 4.5 Intercellular/intracellularpercentage (IIP) = area of intercellular/area of intracellular*100%.Treatment ratio = IIP by treatment A/IIP by treatment B (results roundup to one decimal). *Example: 3.1 = 29.6/9.4 = IIP of IR/IIP of Fresh

TABLE 2 SEM quantification for pears Intercellular/intracellularTreatment percentage (%) Ratio IR 7.5 Fresh 4.1* 30.8 IR 1.0 10.4** Lye3.0 7.1 Knife 4.3 *Example: 4.1 = 30.8/7.5 = IIP of IR/IIP of Fresh**observation of sever destruction of cell wall structure due to lyepenetration

EXAMPLES Example 1 IR peeling of Tomatoes with Catalytic IR Emitters

Due to the variance in harvest time of different cultivars of tomatoes,three commonly grown cultivars (cvs.), Sun6366, CXD179 and AB2, ofprocessing tomatoes (Lycopersicon Esculentum) were used for this study.They were grown by a commercial grower (Button & Turkovich Co., Winters,Calif.) in 2008 season and were hand harvested at red-ripening stage.Tomatoes considered to have defects based on visual observation wereeliminated and only tomatoes with uniform sizes were used in theexperiments. Tomatoes were washed by tap water and their surfaces weredried with paper towels. In order to avoid chilling injuries, tomatoeswere stored no longer than 4 days in an incubator at 11±1° C. beforebeing used for the peeling study. Due to high variation in weight,tomatoes that fell into the range of 70 to 110 g were used. The diameterof tomatoes at the largest transverse section was measured and theaverage was found to be 49±3 mm. The average height of tomatoes, whichwas determined from the stem scar to the blossom end, was 63±9 mm.Different tomatoes cultivars were used for different sets of testsdepending on their harvest date and experimental schedule.

Peeling Performance

The ease of peeling was evaluated according to Mohr (1990) with somemodification. The grading system based on a scale of 1 (unable to peel)to 5 (easy to peel), was used to describe the easiness of peeling oftomatoes heated under different conditions (table 3). A score greaterthan 4 was considered as an acceptable level for peeling easiness. Thismethod is considered to be more sensitive compared to other mechanicalevaluation methods for evaluation of peel loosening.

Peelability was used to determine the degree of peel removal andcalculated as un-removed peel per unit weight (cm²/g). According to FDAstandard (21CFR 155.190), un-removed peel per gram of the raw productshould be less than 0.015 cm2/g. This value was used in this study as astandard to determine whether the tomatoes were fully peeled or not. Tomeasure the peelability, the residual skins on each peeled tomato wereremoved with a knife and then were aligned onto the grids of a sheethaving each squared mesh of 9 mm2. The number of meshes was used tocalculate the area of the residual peel.

Peeling loss, the weight change of tomato before and after peeling interms of percentage, was used to determine the amount of tomato that wasremoved as by-product or waste (Garcia and Barrett, 2006a). It isdesirable to have a low peeling loss from a peeling process.

Product Quality

Texture is one of the most important quality indicators of peeledtomatoes. A procedure developed in the Plant Science Department atUniversity of California Davis was used to characterize the firmness oftomatoes (Cantwell, 2006). The firmness of tomatoes (N) was measuredusing a fruit texture analyzer FTA GS-14 (Texture Technologies Corp.,Scarsdale, N.Y.) through a compression test. A 25-mm diameter probe withflat surface was used to compress the horizontally aligned whole peeledtomato to a distance of 5 mm under 5-mm/s forward speed. The color ofpeeled tomato was also measured at three different locations along thetransverse direction. Tomato color was determined in L* a*b* color spaceusing Minolta Chroma Meter CR200 (Minolta Crop., Ramsey, N.J.).According to Cantwell (2006), Hue° is considered to be the mostappropriate value to measure tomato color rather than the individualchromatic components. Hue° was calculated using equation 1:Hue°=tan⁻¹(b*/a*)

TABLE 3 Definitions of peeling easiness Grade Scale Description 1Removal of the peel is too difficult; some areas fail to peel off orlarge amount of flesh remains on skin 2 Removal of the peel is difficultin most area of tomatoes; certain areas may not be peeled off 3 Removalof the peel is possible but some difficulties may exist at certainlocations 4 Removal of the peel is possible with little effort; largepiece of peels can be removed smoothly 5 Removal of the peel is possiblewithout any difficulty; large piece of peels can be removed quickly andsmoothly

The surface temperature of tomatoes was an important processingparameter related to peel-loosening and degradation of pectin undertomato skin. Thus, the skin temperatures of the tomatoes at various IRheating times were measured using a non-contact IR thermometer (LesmanInstrument Company, Bensenville, Ill.). The reported temperature was themean value of temperatures at four different positions on each tomato(two on the sides, one on blossom end, and one on stem scar). For lyepeeling, the surface temperature of tomatoes was assumed to be equal tothe temperature of peeling solution.

IR Peeling of Tomatoes

Regular lye peeling with NaOH was used as a control for the IR peeling.Tomatoes were dipped into 10% (w/v) NaOH solution at 95±2° C. for 30,45, 60, and 75 s to simulate the typical industrial operation. The ratioof lye solution to tomato was 5:1. In order to prevent any cookingeffect due to heating by the peeling solution, tomatoes were thensubmerged into a beaker containing tap water at room temperature for 30s after the heating.

An IR heating system equipped with two catalytic IR emitters (CatalyticDrying Technologies LLC, Independence, Kans.), and powered by naturalgas, was used in this research. The IR emitter has a heating surface of300×600 mm. A custom-designed circular metal holder attached to a screwrod was used to place tomatoes between the vertically aligned emitters.The screw rod enabled the horizontal rotation of tomato for 90° every 15s to improve heating uniformity. The schematic of the experimentaldevice is shown in FIG. 1. Based on our preliminary tests the distancebetween the emitters significantly affected the peeling loss and peelingperformance, thus the distances between the emitters were selected as90±2 mm, 110±2 mm, and 120±2 mm for the tests. Tomatoes were heated withIR for 30, 45, 60, and 75 s. The rotation effect on the product qualityand the peeling performance were investigated.

Statistical Analysis

Analysis of variance (ANOVA) and mean separation by Duncan's multiplerange tests (p<0.05) were applied to compare the treatments using SASsoftware package (SAS Institute, 1992). All reported values are theaverage of ten replicates. All tests were completely randomized so as toobtain independent observations.

Results of Tomato Studies

IR Peeling

Lye Peeling of Control Samples

For cv. Sun6366 the ease of peeling and peeling loss increased with theincrease of dipping time for lye peeling (table 4). Even though alldipping treatments met the 0.015-cm2/g requirement of peelabilitystandard, we observed that at least 45 s is needed to achieve acceptablelevel of the easiness of peeling. In contrast, the cv. CXD179 neededless dipping time to achieve a similar easiness of peeling and showed ahigher firmness. The firmness did not change much when the easiness wasabove level 4. The colors of the tomatoes were relatively stable underdifferent heating durations. The results indicated that differentvarieties had different peeling performances and product qualities.

TABLE 4 Effects of lye peeling time on quality and peeling performancefor tomato varieties of Sun6366 and CXD179. Ease Peel- Peeled MethodsPeel- of ing Peeled Firm- and ability Peel- Loss Color ness CultivarConditions^([a]) (cm²/g) ings^([b]) (%) (Hue°) (N) Sun6366 Lye₁₀ 30s.004 3.5a 11.5 29.1 14.7a Sun6366 Lye₁₀ 45s .008 4.1a,b 11.7 29.4 12.7bSun6366 Lye₁₀ 60s .004 4.7 b 13.4 29.5 13.7b Sun6366 Lye₁₀ 75s .003 4.9c13.6 29.6 12.7b CXD179 Lye₁₀ 30s .007 4.3 10.7 31.5 16.7 CXD179 Lye₁₀45s .002 4.5 12.7 30.0 16.7 Subscript 10 of Lye₁₀ indicates thepercentage of lye concentration in the lye solution. Means withdifferent letters in each column for each variety are significantlydifferent at P < 0.05 level.

Peeling of Tomato Cv. SUN6366

When IR was used for peeling with an emitter distance of 120 mm (table4), the required IR heating time to achieve an ease of peeling scoreabove 4 was 60 s which was about 15 s longer than the lye peeling.Compared to the control, the IR peeled tomatoes had much firmer textureand much less peeling loss, such as when the ease of peeling was above4, the IR and lye peeled tomatoes had firmnesses of 14.7-17.5 and12.7-13.7 N, respectively, and the corresponding peeling losses of7.3-9.8% and 11.7-13.6%. All peeled products met the standard ofpeelability. In general, the rotation seemed to improve both theeasiness of peeling and firmness and also reduced peeling loss, but didnot have significant effect (P<0.05) on peeling performance and productquality.

Because of the parallel configuration of the emitters used in thisexperiment, rotating the tomato facilitated uniform surface heating ofthe tomato and thereby the penetration IR into the tomatoes to achieveminimum heating time. For industrial production, it a differentconfiguration of IR emitters may be used to eliminate the need fortomato rotation and achieve uniform heating of the tomato surface.

Peeling of Tomato cV. CXD179

For cv. CXD179, all IR peeled tomatoes met the peelability requirement(table 4). The heating rate and firmness of peeled products wereimproved when the emitter gap was reduced from 110 to 90 mm. Therefore,in order to provide higher heat fluxes to rapidly heat the surface oftomatoes, relatively smaller gap between emitters is generallyrecommended, but consideration should be given to cultivar differencesas indicated by comparing the data on product surface temperaturefollowing IR heating (tables 3 and 4). For instance, the surfacetemperature of the tomato was 75° C. for emitter gap of 120 and 90 mmfor Sun6366 and CXD 179, respectively. The easiness value of peelingreached to 4.8 and was significantly higher (P<0.05) than the control(4.5) when heating time was 45 s. However, the firmness of IR peeledtomatoes was in the range of 12.7 to 15.7 N, while the control gave 16.7N for both results in table 2. The lower firmness of IR peeled tomatoescould be due to long exposure to IR heating. The average peeling loss ofIR treated tomatoes was approximately 9% which was significantly lower(P<0.05) than that of control which was around 10.7%. The difference inpeeling loss will likely be greater when the peels are removed by amechanical peel eliminator in the industry. The color of IR peeledtomatoes was similar to the control.

Example 2 IR peeling of Peaches Catalytic Emitters Materials

Clingstone peaches (Prunus persica) without visual defects were used inthis study.

The geometrical characteristics of peaches are very important for IRpeeling and were measured by using a digital caliper to determine thetotal height, diameter in cheek direction, diameter in suture direction,diameter at 45° away from suture, and shoulder height, as well as theheight, width, and thickness of pit (shown in FIG. 1). We also measuredthe other physical and chemical attributes of fresh peaches, includingfruit weight, volume, density, firmness, color, surface area, andsoluble solid content and used the information for calculation ofpeeling performance. The sugar content of fresh peaches was determinedusing a refractometer (N-50E, Atago, Tokyo, Japan) with a referencetemperature of 23° C.

Peeling Procedures

Lye Peeling

Lye peeling was used as a control for the IR peeling. Peaches were firstdipped into 3% (w/v) KOH solution with a temperature of 95±2° C. for 3seconds and then were immediately placed into a steamed chamber with anaverage temperature of 70±4° C. for 39 seconds, which simulates thetypical industrial process. After the heat treatment, each side of thepeach was sprayed for three times with water at a pressure of 350 kPa/50psi to remove the skin. To further explore the peel removal potential,the partially peeled peach was hand-scrubbed by a trained technician andwas dried with paper towel.

IR Peeling

An infrared heater equipped with two catalytic IR emitters powered bynatural gas was used in this research. Each emitter has a surface areaof 30×30 cm and an intensity of 8000 W/m². To place the peach in theheater, a custom-designed metal rod holder was used and attached to thetip end of the fruit. The peach was located at the center between of theIR heating emitters (FIG. 4). Based on our preliminary tests, the testeddistances (gap sizes) between the emitters were selected as 90±2, 115±2and 140±2 mm for studying the effect of gap size on peeling performancewhen medium size peach (65 mm diameter in cheek direction) and heatingtimes of 90, 135 and 180 seconds were used. To study the effect ofheating time, we tested five heating periods, 60, 90, 120, 150, and 180seconds, using medium size pear and gap size of 115 mm. To examine theeffect of peach size, we used peaches with three sizes, 60±1 mm, 65±1mm, and 70±1 mm under gap size of 115 mm under three heating timeperiods, 90, 135 and 180 seconds. The initial temperature of peachesbefore heating was 23±2° C. (room temperature). All tests were conductedwithin two days after the peaches were received. Peaches used in thesecond day were stored in an incubator at 2±1° C. during the night andthen tempered in the room condition before testing. To remove the skinof IR treated peaches, the same peel removal procedures adopted for lyepeeling were also applied for IR peeling.

Peeling Performance and Product Quality Evaluation

Peeling Performance

Peelability (%) was calculated by dividing the un-removed peel area bytotal fruit surface area and expressed as percentage. The un-removed(residual) skin area on a peeled peach was determined by using a sheetwith grids and a USDA standardized square-grid plate with known area.Peach total surface area was predicted based on corresponding fruitweight using a regression model we developed.Peeling yield (%) is the weight difference of a peach before and afterpeeling divided by original weight and expressed as percentage.Moisture loss (%) is the weight difference of a peach before and afterIR heating divided by the original weight and expressed as percentage.It reflects the amount of moisture evaporated during IR heating.Heat ring depth (mm) is a measure of excessive heating causing colorchange at outer periphery of peach flesh. It was determined by observingcolor change of peach after it was cut.

Product Quality

Color (surface color of fresh and peeled peaches) was measured at threedifferent locations along the fruit transverse direction in the CIEL*a*b color space using a Minolta Chroma Meter CR200 (Minolta Crop.,Ramsey, Japan). All color readings of peeled fruits were takenapproximately 5 min after peeling. The color difference was calculatedusing Eq. (1) and a smaller value indicates less color change before andafter peeling.

$\begin{matrix}{{\Delta \; E} = \left\lbrack {\left( {L^{*} - L_{0}^{*}} \right)^{2} + \left( {a^{*} - a_{0}^{*}} \right)^{2} + \left( {b^{*} - b_{0}^{*}} \right)^{2}} \right\rbrack^{\frac{1}{2}}} & (1)\end{matrix}$

For fresh, before color measurement the skin (0.5 mm thickness) wasremoved with knife. The same area was used for texture measurement.

Texture (firmness of peaches) was measured by using a fruit textureanalyzer FTA GS-14 (Texture Technologies Corp., Scarsdale, USA) based ona puncture test. A 7.9 mm diameter round-ended probe was used to punchthrough the peach fruit (see figure below) to a distance of 10 mm undera 5 mm/s forward speed.

The surface and internal temperature profiles during IR heating andafter heating were determined using thermocouples (FIG. 5) (hypodermicminiature type-T thermocouples (HYP1, Omega Engineering, Inc., Stamford,Conn.) with a wire diameter of 0.3 mm), sensing bead diameter ofapproximately 60 um, and response time of 1.5 ms). HH147 data logger(Omega Engineering, Inc., Stamford, Conn.) was used to record thetemperature change. We measured the surface temperatures at fourdifferent locations, including a point on the cheek of peach which isclosest to the surface of the top IR emitter, a point on the suture ofpeach which is along the same longitude of the cheek point, each pointfrom tip and stem end of peach fruit, which are along the same latitudeof the cheek point. The four locations for the internal temperaturemeasurements were 2, 4, 8, and 16±0.2 mm below the peach surface.

Statistical Analysis

Relationship between surface area of each individual peach and itsweight was predicted through linear regression analysis. All reportedvalues are the average of ten replicates.

Results

A result summary of the determined physical parameters of peaches isshown in Table 5. The mass and surface area varied from 101.4 to 255.6 gand from 10156.4 to 18152.7 mm², with mean values of 150.6 g and 13791.6mm², respectively. Dimensions varied from 55.4 to 79.4 mm in totalheight, 53.9 to 74.9 mm in the direction of suture, and 54.4 to 83.3 mmin cheek thickness, with average values of 66.3, 64.5, and 65.9 mm,respectively. Mean of the diameter of 45° away from suture direction wasslightly higher than the other measures because of the indentedirregular shape at the suture. The means of three-dimensional size ofpit (i.e. length, width, and thickness) were 36.0, 19.4, and 25.5 mm,which did not change significantly for different size of fruits. Wholefruit volume and density varied between 106.2 and 270.4 cm³ and between0.897 and 0.985 g/cm³, with average value of 157.3 cm³ and 0.957 g/cm³,respectively.

TABLE 5 Geometrical properties of peaches (n = 149) Volume and FruitDimensions Density Total D- D- D-45 Peach Peach Surface Pit DimensionMass SH Height suture thickness deg. Volume Density Area Length HeightWidth Stat. (g) (mm) (mm) (mm) (mm) (mm) (cm3) (g/cm3) (mm2) (mm) (mm)(mm) mean 150.6 9.7 66.3 64.5 65.9 67.0 157.3 0.957 13791.6 36.0 19.425.5 std 31.5 1.2 4.6 4.0 5.9 5.0 32.6 0.016 1573.5 2.6 3.5 2.7 max255.6 13.2 79.7 74.9 83.3 82.1 270.4 0.985 18152.7 42.1 37.3 38.1 min101.4 5.7 55.4 53.9 54.4 55.7 106.2 0.897 10896.4 26.0 15.7 5.7

It was found that 80% of fruit had weight below 178 grams and sizes lessthan 73 mm. Because the cheek thickness of peach is an importantparameter for IR peeling, the distribution of fruit mass and thethickness (diameters in cheek direction) is plotted in FIG. 3. Based onthe size (cheek thickness) distribution, we classified the fruits intothree groups, i.e. small, medium, and large, with average values of 60,65, 70 mm, respectively. For the samples used for peeling tests, peachesin each group had a size variation range of 4 mm.

IR Peeling—Effect of Heating Time

The tests were conducted with peach size of 60 mm and emitter gap sizeof 115 mm. The peaches were partially peeled with hand scrubbing afterIR heating up to 90 seconds (FIG. 4). The heating time had significanteffects on the peelability, peeling yields, peeled peach firmness andcolor changes. At the heating time of 180 sec, the peelability reachedabout 80%, but the peeling yield was lowered due to moisture loss andpeel removal. In general, compared to IR peeling, lye peeling had higherpeelability and yields, but caused more color change which is notdesirable. Based on this set of test, it is concluded that minimum IRheating time of 90 seconds is necessary to achieve significant amount ofpeel removal. The depth of the heating ring increased with increasing ofIR heating time (FIG. 5). It is desirable to eliminate or minimize theheating ring after peeling, which might be achieved by reducing the IRheating time by increasing IR intensity and/or changing theconfiguration of IR emitter.

Effects of Peach Fruit Size

To determine the effect of fruit size on peeling performance, theemitter gap was set at 115 mm and three heating times were tested. Thethree sizes (60, 65, and 70 mm) of peaches performed differently (FIG.6). The IR peelability increased with the increased of peeling time andreached maximum of 87%. The small size peaches had lower peelability dueto less heating because the fruit surface was farther away from theemitter surface. But they had a higher peeling yield due to less peelremoval (FIG. 7). The firmness of both IR and caustic treated peacheswas lower than fresh peaches (FIG. 8) and the color changes of peeledpeaches were similar regardless of the peeling methods (FIG. 9).Moisture loss increased with the increase of IR heating time for allsizes of peaches while the smaller the fruit had the higher the moistureloss which could be due to large surface area to volume ratio (FIG. 10).

Effect of IR Emitter Gap

Three emitter gap sizes, 90, 115 and 140 mm, were tested using mediumsize peaches (65 mm) under three heating times (FIG. 11). When the gapsize was reduced from 140 mm to 115 mm, the peelability wassignificantly improved. The peeling yields also showed a trend ofimprovement with gap reduction. By reducing the gap to 90 mm, the IRtreated peaches achieved a similar peeling yield as caustic peeling andhad maximum peelability of 85% (FIG. 12). The reduced gap size mightprovide more uniform heating on the peach surface (FIG. 13). All testedpeaches under different gaps had similar color changes. Furthermore, itwas observed that the smaller gaps of IR treatments resulted in slightlylower peel firmness than the selected caustic peeling (FIG. 14). Underthe smaller gap level of IR treatment, peelability and peeling yieldsincreased as the heating time increase. This indicates that a narrowergap, longer time and more uniform heating was correlated to a betterpeeling performance.

Temperature Distribution

FIG. 15 shows the changes in temperature at four locations on the peachsurface during and after IR heating. The vertical line denotes the endof 180 seconds of IR heating. The results indicated that surfacetemperature increased quickly during IR heating and continued toincrease for a short time even though the peach was removed from theheater, finally decreased. There was a maximum temperature difference ofabout 20° C. among the different locations. This demonstrated that it isnecessary to improve the heating uniformity in the future. One of theways to improve the heating uniformity is to design the emitter withcurvature profiles similar to that of the peach shape.

The internal temperature distribution showed that there was a hugedifference at different locations (FIG. 16). The temperature at 2 mmbelow the surface was similar to the surface heating profile, but muchhigher than that at 4 mm. This indicated that the IR heating mainlyheated the surface layer. The low temperature in the peach is desirableto achieve high quality product with high firmness. If the IR intensityis increased, the required heating time could be reduced, which wouldlead to reduced heating ring.

Example 3 IR Peeling of Pears Using Ceramic Emitters Peeling Procedures

The weights of Bartlett pears used in the test were in the range of130-332 g. For infrared heating of pears a vertical emitter setup wherethe emitter plates were parallel to one another was used (FIG. 17). Theemitters were placed with a gap of 3.85 inches between them. A rotatingrod was placed on a base beneath the emitter stand and was used torotate the pears. All pears were placed upright on the rod and rotatedduring their time in the emitter. The rotating rod was marked andemitters remained untouched so the setup was centered at all times.Testing was carried out on medium size pears placed in the infraredemitter setup for 60, 45, 30, 25, and 15 seconds. 10 Replicates werecarried out for each period of time that was experimented with.

Peeling was conducted using hand scrubbing. Each pear was hand scrubbedby the same person using only the thumb below the knuckle to rub theskin off and was done using running water. Due to the nature of a pears'geometry it was deemed unpractical to set a time for hand scrubbing andpeel removal however, no area of pear was subjected to peeling otherthan an initial one-time go over. Peel removal took place over a finesieve so all removed peel was caught, strained from any possible waterretention and set aside for observation.

Peel Removal

As time of IR heating increases the amount of pear peel remainingdecreases. The pear peel completely glided off at both 60 seconds asseen in FIG. 18 A, and 45 seconds as seen in FIG. 18B. In both casespeel separated from the fruit in large pieces as seen in FIG. 19. Thepeel only needed an initial tear in the peel made by hand scrubbing andwith a swipe of the thumb was easily removed. At 30 seconds the peel wasremoved easily but clung to the stem and root of the pear (FIG. 20). Theheating of 30 seconds lead to fragmented peel pieces.

FIG. 20 B contains images of Bartlett pears depicting 25 seconds of IRtreatment. The majority of the peel was removed with the most peel clingoccurring at the stem, root and on any scars present on the pear. Peelwas removed in fragmented pieces in most cases and did need slightlymore pressure to remove compared to 60/45 seconds of heating.

IR Heating of 15 seconds yielded many small fragmented pieces of skinand slightly more pressure (firmness) than 25 seconds of IR treatment inscrubbing to remove the peel. There was a significant area of peelremaining compared to alternative IR times, however, there was still aconsiderable portion of peel removed. These results are seen in theimages listed in FIG. 20 C. This shows promise for future infraredheating peeling designs, which may be able to distribute heat moreuniformly.

Cooking Rings

After peel removal pears were sliced in half length-wise in order tomeasure the cooking ring. The cooking ring was measured at the shoulderof the pear. It was noted that the cooking ring appeared even throughoutthe length of the pear regardless of the diameter of the pear whenexcessive heating was used. Surprising cooking rings were not obviouslyapparent for infrared heating times of 30 seconds or less. Cooking ringswere most apparent at 60 seconds. In general cooking ring thicknessdiminished as IR heating time decreased.

An optimum time of between 15 and 25 seconds of heating produced highquality products and could be significantly reduced with the design of amore efficient infrared system. Surprisingly pear peel could becompletely removed with infrared heating application followed by gentlemechanical application to solve any issues of minor peel cling or scarformation.

Sensory Evaluation

The sensory evaluation comparing diced pears peeled with caustic versusinfrared peeled pears in extra light syrup was conducted by 5 trainedpanelists. On a 5 point scale, appearance was rated acceptable (3points) for caustic peeled pears compared to typical (4 points) forinfrared peeled pears. Texture was rated less acceptable for causticpeeled pears compared to infrared peeled pears. Taste and the overallfinished product was rated comparable between caustic peeled pears andinfrared peeled pears.

Example 4 Comparison of Tomato Peel Micro-Structure Changes after IR,Steam and Lye Peeling by Using Cryo-Scanning Electron Microscopy TomatoOuter Surface Changes

On fresh tomato surface, extracelluar cuticle covers the outer surfaceof tomato skin as a continuous waxy membrane. From the SEM images, itcan be seen that clearly defined contours of cell wall structures existson fresh tomato surface (FIG. 21 A). The steam peeling yielded a similarappearance (FIG. 21 D). After lye treatment, the contours and overallshape of epidermal cells became more readily visible and also raisedsurfaces in the center of each cell appear differently from the concavesurface on the cells of fresh tomatoes (FIG. 21 C). In contrast to lyetreated tomato, the skin treated by IR showed that distinct cellcontours disappeared and a knoblike protuberance arising from each cellsurface (FIG. 21 B). These knoblike protuberances are unique to IRpeeled fruits and vegetables.

Example 4 Continued Tomato Tissue and Microstructure Changes

A cross-sectional SEM images of the outer pericarp tissues for thefresh, IR-, lye- and steam-treated tomatoes are presented in FIG. 22.The tomato dermal system, or called as exocarp, comprises cuticle,single tabular form epidermis layer plus two to four layer ofthick-walled hypodermal cells. Beneath the exocarp tissue, the cellstructures become larger with a form of round shape, which were known asparenchymatous cells and represented the edible flesh portion of tomatofruits. By comparing FIG. 22 A and FIG. 22 B, thermal expansion of cellwall and separation of cytoplasm from cell membrane can be obviouslyfound in FIG. 22 B. These anatomical features indicated that IR thermaltreatment had dramatically disrupted the microstructure of tomatotissues right beneath the skin. Cell wall expansion was only observed inIR treated tomatoes, not in lye and steam treated tomatoes (FIGS. 22 Cand 22 D), however, cytoplasm separation and enlarged intercellularspace can be found in lye treated tomatoes which could be due to thedegradation of pectin layer in the middle lamella dissolved by lyesolution. Cell wall thermal expansion in steam treated tissues was foundinsignificantly due to the inefficient heat delivery and transfercapability of steam as compared to IR.

Tomato Pericarp Cells Changes

A higher magnification SEM images in FIG. 23 C revealed that control andlye treated tomato tissues had crystal structures in their cytoplasm andthicken cell walls. No crystal structures were found for IR treatedsamples in FIG. 23 B. Different from IR and lye treated tissues in FIG.23 D, cytoplasm in steam treated samples showed more solid content whichresult from the steam water diffusion. Steam water can breakdown thecell structure according to conduction heat transfer coupled with thediffusive mass transfer.

Example 5 Comparison of Pear Peel Micro-Structure Changes after IR,Knife-Cut and Lye Peeling by Using Cryo-Scanning Electron MicroscopyPear Outer Surface Changes

Appearance of the outer surface of pear skins was dramatically changedafter IR and lye peeling. In contrast to fresh control with smoothsurface with little cracks, visible bubbles appeared on the pear skinsheated by IR. It is suspect that the occurrence of such bubbles resultsfrom the phenomena of evaporation and diffusion of water vapor from thetissue beneath the skin to the outer surface impacted by the IRirradiative heating. More cracks but fewer bubbles were found on theskin treated by the hot lye solution. These cracks damaged due to thehigh concentration and high temperature of lye solution would facilitatelye penetration during peeling process, which cause the peel beingdissolved faster and more completely.

Cross-Sectional View of Microstructure Changes of Pear Tissue

Different mechanisms responsible for different peel-removal methods wereclearly shown and compared to fresh pear tissues in FIG. 25. Absence ofthin epidermal cell layers was found in pear samples treated byknife-cut peeling and hot lye peeling. In the FIG. 25 D of knife-cutsamples, small and tabulated epidermal cells did not exist and large andround shaped percarp cells remained with little deformation. This istrue because rupture force of knife-cut occurred only at the pear skinwith a thickness of about 1 mm while the cells apart from that layerhave less mechanical damage and appears intact. As a comparison,completely disrupted cells with unclearly defined cell walls wereobserved in lye peeled pear samples. Skins with the outer part of thepear tissues were gradually dissolved into the hot lye solution, whichcause the disappearance of pear skin and epidermal cells in FIG. 25 C.KOH chemical reactions with pear tissue cause the breakdown of cellwalls and disorder of cell structures. Depending on the diffusion andreaction rate, the degree of cell destruction may vary and affect thepeeling performance and peeled product quality. Complete skin andpericarp tissues were reserved in IR treated samples, in which cellstructural integrity can explain the findings of improved peeled productquality and less peeling loss of IR dry-peeling. Feasibility of using IRheat for fruit peeling was reflected as layer separations in the SEMimages. As shown in FIG. 25 B, the presence of pores beneath the skinresulted from the thermal introduced degradation of pectins withinmiddle lamella and disruption of cell walls.

Pear Pericarp Cells Changes

Closer views of cell structural change due to different treatments wereshown in FIG. 26. Thermal expanse of cell walls and enlargement of intercellular space can be clear seen in IR treated samples (FIG. 26 B).Disordered cells and lost structures after lye peeling were obvious incontrast to the well defined cell wall and organized cell alignment offresh pear. As seen in FIGS. 26 A and 26 D, smaller cells closed to skincan be observed in fresh samples but were absent after knife-cut.Therefore, undesired removal of tissues attached to the skin can explaina larger peeling loss rate due to mechanical peeling method.

We claim:
 1. A method for peeling fruits or vegetables comprising (i)exposing the fruit or vegetable to heat from at least one concaveinfrared emitter or plurality thereof (ii) wherein the distance betweenthe fruit surface and the emitter surface is between 5-40 mm (iii) andthe surface temperature of the fruits and vegetables during and after IRheating is 70-100° C. for a time sufficient to promote peeling and atissue ratio of intercellular/intracellular area ranging from about 25%to 33%.
 2. The method of claim 1 wherein the emitter is ceramic.
 3. Themethod of claim 2, wherein the ceramic emitter consists of an array or zconfiguration.
 4. The method of claim 1 wherein the fruit or vegetableis exposed to the emitter while rotating the fruit.
 5. The method ofclaim 1 wherein the fruit or vegetable is selected from the groupconsisting of pear, peach, apricot, apple, grape, cherries, tomato,bananas, potato, eggplant, tomato, cucumber, zucchini, oranges, lemons,grapefruit.
 6. The method of claim 1 wherein the emitter surfacetemperature is in the range of 200-850° C.
 7. The method of claim 1wherein the fruit or vegetable passes through multiple emitter zones ofsame or varied temperatures.
 8. An apparatus for dry peeling of fruitsand vegetables comprising a conveyor system for delivery of the fruit orvegetable to an area containing at least one concave infrared emitter orplurality thereof wherein the emitter temperature is 200-850° C. and thedistance between the fruit surface and the emitter surface is between5-40 mm.
 9. The apparatus of claim 8 further comprising a rotating standfor the fruit or vegetable within the area heated by the emitter. 10.The apparatus of claim 8 wherein the emitter is ceramic.
 11. Theapparatus of claim 8 wherein the conveyor system contains recessed wellsfor holding the fruit or vegetable and promoting uniformity of heatexposure.
 12. The apparatus of claim 8 which is encased in a metalhousing and may contain an air circulation mechanism to facilitateuniform distribution of heat during processing.
 13. An apparatus ofclaim 8 wherein the apparatus contains multiple emitter zones of same orvaried temperatures.